Python: [BREAKING] added SerializationMixin and applied to contents, agents, chat client… (#1012)

* added SerializationMixin and applied to contents, agents, chat clients, removed AFBaseModel

* fix annotations type

* mypy fixes

* fix tests

* fix serializable subvalues and added large docstring

* updated indents in code block

* fixed exported urls

python/packages/lab/lightning/samples/train_math_agent.py

@@ -168,7 +168,7 @@ async def math_agent(task: MathProblem, llm: LLM) -> float:
         MCPStdioTool(name="calculator", command="uvx", args=["mcp-server-calculator"]) as mcp_server,
         ChatAgent(
             chat_client=OpenAIChatClient(
-                ai_model_id=llm.model,  # This is the model being trained
+                model_id=llm.model,  # This is the model being trained
                 api_key=os.getenv("OPENAI_API_KEY") or "dummy",  # Can be dummy when connecting to training LLM
                 base_url=llm.endpoint,  # vLLM server endpoint provided by agent-lightning
             ),

python/packages/lab/lightning/samples/train_tau2_agent.py

@@ -103,14 +103,14 @@ class Tau2Agent(LitAgent):
         assistant_chat_client = OpenAIChatClient(
             base_url=llm.endpoint,  # vLLM endpoint for the model being trained
             api_key=openai_api_key,
-            ai_model_id=llm.model,  # Model ID being trained
+            model_id=llm.model,  # Model ID being trained
         )
 
         # User simulator: uses a fixed, capable model for consistent simulation
         user_simulator_chat_client = OpenAIChatClient(
             base_url=openai_base_url,  # External API endpoint
             api_key=openai_api_key,
-            ai_model_id="gpt-4.1",  # Fixed model for user simulator
+            model_id="gpt-4.1",  # Fixed model for user simulator
         )
 
         try: